(1) Field of the Invention
The present invention relates to a method and an apparatus for plasma-etching, and more particularly to a method and an apparatus for etching surfaces of an object such as a semiconductor wafer with plasmas produced by utilizing a high frequency electric field.
(2) Description of the Related Art
As conventional plasma-etching apparatuses of the kind to which the present invention relates, two examples can be referred to for reference.
The first example which is an etching apparatus as shown in FIG. 1 has been disclosed in Japanese Patent Application Kokai Publication No. Sho 56-155535. In this apparatus, an object 101 to be etched is set on a table (wafer holder) 102 in a plasma generation chamber 103 so that it is placed in tile electron cyclotron resonance discharges caused by microwaves 104 and is subjected to an etching process. In the drawings, numeral 105 denotes a gas inlet duct, 108 denotes a magnetic coil, 109 denotes microwave inlet window, 110 denotes a waveguide, and 114 denotes an electron cyclotron resonance point.
The second example which is an etching apparatus as shown in FIG. 2 has been disclosed in Japanese Patent Application Kokai Publication No. Sho 60-134423. In this etching apparatus, a reaction gas is introduced into a plasma generation chamber 203 through a gas inlet duct 205. A reactive gas plasma is so produced in the plasma generation chamber 203 that both the microwaves generated by a microwave source (for example, a magnetron) 207 and the magnetic fields generated by magnetic coils 208 act on the introduced reaction gas. The reactive gas plasma thus produced is introduced through a port 212 into a reaction chamber 200 below the plasma generation chamber 203, where a wafer (object) 201 to be etched is placed on a table 202, by utilizing the divergent magnetic fields generated by the magnetic coils 208. In the drawings, numeral 210 denotes a waveguide, numeral 209 denotes a microwave inlet window through which the microwaves generated by the microwave source 207 are introduced into the plasma generation chamber 203, and 215 denotes an electron cyclotron resonance point.
However, there have been problems in the conventional apparatuses as described above in that, although the control of ion energy reaching a surface of the object to be etched is possible by controlling the power of RF waves, the controllable range of dissociation process in plasmas is narrow and, therefore, the extent of controllable etching reactions on the surface of the object wafer is narrowly limited. Also, since the magnetic fields are present in the plasma generation chamber 203 for high density plasmas, there inevitably occurs a magnetohydrodynamic plasma instability due to, for example, drift waves generated in the plasmas, which leads to a problem wherein the ion temperature rises and the directions of ion motions become nonuniform. Further, the problems include a degradation of a gate oxide film and a distortion of etching profile due to the charges accumulated on the wafer.